Modern electrical devices, such as computers, cellular phones, and personal digital assistants (PDAs), include electrical components that may be powered by regulated direct current (DC) supply voltages of specific values, when the only electrical power available may be from a different DC voltage source having a voltage level different from the DC supply voltage or voltages desired. Further, the available DC voltage source may be substantially unregulated. For example, in desk-top computers, unregulated DC voltages are typically derived from alternating current (AC) mains by rectification and crude filtering to produce a voltage source having an average DC value with a substantial ripple corresponding to the mains AC frequency. This unregulated voltage is typically different in magnitude from the voltage or voltages required to power the various components in the computer. In battery operated devices, such as lap-top computers, cellular phones, or PDAs, the voltage supplied by the battery may vary substantially over time, and it may be of a different value than the voltage or voltages required to power the individual components of the device.
Power converters, such as switched-mode DC-DC converters, are often used in such applications, as they provide improved efficiency over dissipative conversion methods. In such switched-mode DC-DC converters, an unregulated input voltage is converted into a periodic pulse waveform that has an average value which varies with the ratio of the pulse width to the pulse period. This conversion is typically performed by controlling the states of several switches, such as field effect transistors (FETs), connected between the input voltage and particular device. By controlling the states of the various transistors, a desired average current can be impressed through the inductor and thus efficiently control the power flow between the power source and the load.
Two important parameters in the performance of such converters are gate drive losses (QG) and resistive losses (I2RON) of the switch FETs. Resistive losses are most significant when the converters are operating at high loads (i.e., currents). Conversely, at lower loads, gate drive losses are dominant because of the small amounts of current flowing through the converters decrease the resistive losses. In order to maximize converter performance, attempts are often made to minimize and balance these losses by optimizing the FET sizes.
Accordingly, it is desirable to provide a power converter with improved efficiency with respect to gate losses and resistive losses. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.